This solar geoengineering idea has a Goldilocks problem

Geoengineering clouds requires considerable cooperation from the clouds. Credit: NOAA

This summer’s barrage of extreme weather around the globe - including record heat waves, wildfires, and flooding - have amplified calls for urgent action to address climate change. The view that rapid, drastic reductions in greenhouse gas emissions are needed is now the scientific consensus. More controversial are calls for investigating geoengineering techniques that may cool the planet quickly by reflecting sunlight away from Earth’s surface. 

One technique, called marine cloud brightening, would seek to make low-level clouds over the ocean more reflective and longer-lived by injecting them with small particles of salt generated by spraying seawater into the air. Theoretically, water vapor would collect on the surface of these salt particles creating additional cloud droplets that would reflect more sunlight back out to space. 

This may be easier said than done, according to new research published in the Journal of Atmospheric Sciences by NOAA’s Chemical Sciences Laboratory and CIRES researchers. Using a sophisticated computer model that accurately simulates the miniscule changes in cloud droplets, the researchers found that both the size of the cloud seed particles and the number of particles injected are crucial for successfully brightening the clouds to reflect more sunlight. To make matters even more complicated, the optimal particle size is likely case (or cloud) dependent.

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